This invention relates to an antenna. The antenna has a relatively high Pattern Averaged Gain (PAG) figure, and finds particular utility in portable wireless devices such as portable telephones.
PAG is one of several metrics that can be used to characterise antennas. All antennas radiate energy, to a greater or lesser degree, in one or more directions. PAG is one measure of the average transmission characteristics averaged over a full 360° surrounding the antenna. The better the PAG figure, the better the overall transfer of energy from the transmitter via the antenna.
PAG is normally calculated to take into account the dominant polarization intended for a given antenna. For instance, in mobile telephony, the antenna at a Base Station (BS) is generally vertically polarized, and in order to optimize performance, the antenna at the Mobile Station (MS) should be vertically polarized also. However, different people hold their MSs differently, and the relative polarization can differ depending on exactly what position the telephone is held in and whether the MS is held in the left or right hand.
To facilitate comparison between different antennas, during empirical measurements, the MS is arranged so that it is positioned next to a dummy head (to mimic the user's head), and inclined at 60° to the vertical. All PAG measurements and comparisons referred to in this specification were made in this way.
Portable telephones communicate with remote base stations via signals transmitted and received from one or more antennas forming part of the Radio Frequency (RF) circuitry of the telephone. Prior art telephones use a wide variety of different types of antenna depending on a number of factors including size of telephone, cost, performance and bandwidth.
Older portable telephones, and some new ones, use retractable or telescopic whip antennas almost exclusively. Later telephones typically use helical stub antennas or internal planar antennas.
A problem with prior art antennas is their relatively low PAG figures. This effectively means that for a given amount of power input to the antenna, a relatively low power signal is emitted from the antenna (when compared to embodiments of the invention).
The transmitter accounts for the bulk of the power consumed by a portable telephone. For this reason, manufacturers often quote several figures for battery life, depending on what proportion of the time the telephone is transmitting rather than being in a standby mode waiting for a call to be made or received. It is clear from such figures what impact transmission can have on battery life, and hence talk time.
Improvements in PAG for a given telephone by use of a different antenna can therefore have a direct measurable effect on talk time and battery life. Improved PAG can also improve call quality, particularly in areas of poor reception, as the benefits of PAG apply equally well to reception as well as transmission.